Power transmission

ABSTRACT

A valve for automatic stabilization of hydraulic motor speed under varying motor loads is arranged to bypass a small flow around the principal motor speed regulating valve, which small flow is increased with the motor inlet pressure. This compensates for the cross-port leakage in the motor which varies with motor load. The inner parts of the valve may be selectively assembled in various positions to provide various maximum flow openings so that hydraulic motors of various sizes may be effectively stabilized.

' [11] 3,787,027 Jan. 22, 1974 llnited States Patent [191 Curnow et al.

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w nn r ae n TK e 0 l 44 H 99 n 11 i 79 m a m 07 28 a 85 05 .m n 22 P emm 0 n r ut C noll n hwk mNM e r m n C V n I 1 tt V p y RandCorporation, y A orney, Agent, or Fzrm Theodore an Meter Mich.

[73] Assignee:

ABSTRACT [22] Filed: Oct. 16, 1972 A valve for automatic stabilizationof hydraulic motor speed under varying motor loads is arran m PM m d m 8a small flow around the principal motor [52] ing valve, which small flowis increased 25 1/63, 91/452, 137/4925, with the motor inlet pressure.This compensates for the cross -port leakage in the motorwhich varieswith motor load. The inner parts of-the valve may be selectivelyassembled in various positions to provide various maximum ReferencesCited flow openlngs so that hydraullc motors of various sizes may beeffectively stabillzed. UNITED STATES PATENTS 2,020,773 251/63 4 Claims,9 Drawing Figures PATENTED JANZ 2 I974 sum 1 0F 2 PATENIED JAN22|974SEE? 211E POWER TRANSMISSION The US. Pat. to Douglas No. 2,004,522discloses a hydraulic system in which the varying cross-port leakage ofa hydraulic motor is compensated by a pressure responsive valve whichbypasses variable amounts of fluid around the main speed controllingorifice. The range of cross-port leakage which such valves mayaccommodate is relatively limited so that a single valve design cannoteffectively stabilize more than a very limited size range of hydraulicmotors. This has heretofore necessitated a range of stabilizing valvesizes substantially as great as the range of motor sizes to bestabilized.

It is an object of the present invention to provide a single valvedesign which can effectively stabilize any hydraulic motor within a verywide range of sizes.

This is accomplished by the provision of a valve comprising a bodyhaving a longitudinal bore closed at opposite ends, first and secondlateral ports opening to the bore at longitudinally spaced locations,the first port communicating with the bore through slots of-limitedcircumferential width, a spool slidable in the bore having a land tonormally close communication between the ports, tapered grooves in theland adapted to register with the slots in the bore when the spool isshifted longitudinally to establish communication between the ports,piston means at one end of the bore for shifting the spool, spring meansat the opposite end of the bore to bias the spool toward closedposition, means forming a sliding key and keyway between the spoolandthe bore to maintain rotational register between the slots and thegrooves, and means for establishing a plurality of positions of registerto provide a plurality of maximum flow rates when the spool is fullyshifted to open position. 1

IN THE DRAWINGS FIG. 1 is a hydraulic circuit diagram showing in sectiona valve incorporating apreferred form of the present invention.

FIG. 2 is an exploded view of parts of the internal valve mechanism.

FIG. 3 is a cross section online 3-3 of FIG. 1, with one of the partsremoved.

FIG. 4 is a partial cross section'on line 3-3 of FIG. 1 with the partspositioned for greatest maximum flow.

FIG. 5 is a partial cross section on line 5-5 of FIG. 1 with the partsin position for greatest maximum flow.

FIGS. 6 and 7 correspond to FIGS. 4 and 5, but with the parts inposition for medium maximum flow.

FIGS. 8 and 9 correspondwith FIGS. 4 and S, but

with the parts in position for thesmallest maximum flow.

In FIG. 1, a variable displacement pump 10 driven by an electric motor12 withdraws hydraulic fluid from a tank 14 and delivers it through adelivery line 16 to a fixed displacement hydraulic motor 18. The motordischarge line 20 leads to a manually adjustable orifice valve 22 whichdischarges through filter 24 and heat exchanger 26 to the tank 14. Thedelivery line pressure is limited to a predetermined maximum by theusual overload relief valve 28.

The displacement of the pump 10 is automatically regulated so as tomaintain a-constant pressure drop across the orifice 22. This isaccomplished by a threeway pilot valve 30, the spool 32.0f which isexposed at its upper end through line 34 to pressure upstream of theorifice 22 and at its lower end through line 36 to pressure downstreamof the orifice 22. A spring 38 biases the spool 32 sufficiently tomaintain a predetermined small pressure drop across orifice 22. Valve 30controls the displacement of pump 10 through a spring biased servomotor40 by admitting or exhausting fluid to it through the line 42.

The parts thus far described would be adequate to maintain the speed ofthe motor 18 at any constant value determined by the setting of theorifice 22, except that the cross-port leakage, sometimes referred to asthe slip through the motor, varies with variations in load. Tocompensate for this variable slip and thus stabilize motor speed at allload conditions,-a valve 44 is connected in parallel with the orificevalve 22 through lines 46 and 48 and is sensitive to pressure in thedelivery line 16 through a sensing line 50.

The valve 44 has a body 52 with a central bore 54 which is formed by asleeve .56 pressed into the body. Lateral ports 58 and 60 communicatebetween the bore 54 and the connecting lines 46 and 48. Port 58 includesa pair of large holes'62 in the sleeve 56 while port 60 includes a pairof longitudinal slots 64 in the sleeve 56. Slidable within the bore 54is a spool 66 having a land 68 which, in the position illustrated,blocks communication between ports 58 and 60. The land 68 has a pair oftapered grooves 70 which, when the spool is raised, can register withthe slots 64. A similar but smaller pair of grooves 72 are located awayfrom the grooves 70.

The spool 68 contains-at its upper end a pair of keyways 74 whichslidably engage a pair of keys 76 formed in a locating ring78. Thelocating ring 78 is positioned between the upper end of the body 52 andan end cap 80 which contains an adjusting screw 82 for a biasing spring84 which urges the spool 66 downwardly in opposition to delivery linepressure acting on a smallpiston 86. The locating ring 78 may beselectively positioned in any one of several arcuately spaced positionsby means of a-pin 88 which may be received in any one of three holes 90,92 or 94 in the ring 78. Passageways 96 and 98 in the body and the endcap and passage 100 in the spool serve to drain the bottom of the bore54 to the outlet port 60 and the downstream side of the orifice 22. I

In operation with the system filled with fluid and pump 10 driven by themotor 12, at a given setting of the orifice 22 the speed of the 'motor18 at no load will be determined by the biasing force of the spring 38in valve 30 which will maintain a displacement setting of the pump 10such as to maintain a constant pressure drop across the orifice 22 andthus a constant flow therethrough, At no load on themotor 18, thecrossport leakage or slip will be minimal. As the load on the motorincreases, however, the pressure in delivery line 16 willcorrespondingly increase and be transmitted through line 50 to the smallpiston 86, thus raising the spool 66 against spring 84and starting toopen communication from port 58 through. grooves 70 and slots 64 intoport 60. This allows a small amount of additional flow to take placearound the orifice 22 which, if it is equal in amount to the cross po'rtleakage at that particular delivery line pressure, will prevent themotor speed from falling below its no-loadspe'ed. In adjusting to thisnew condition, the pilot valve 30 will act to slightly increase thedisplacement of pump 10 by a corresponding amount.

The degree to which the stablizing valve 44 opens under any givendelivery line pressure can be adjusted over a small range by adjustingthe screw 82 and thus changing the bias of spring 84 upon the spool 66.This, however, is insufiicient to accommodate more than a very limitedrange of values of motor cross-port leakage. A much wider range ofcross-port leakage values may be accommodated by shifting the rotationalposition of the groove 70 relative to the slots 64 as may be seen fromFIG. 7 where the circumferential arc of register between the slots andgrooves is considerably smaller than the full register positionillustrated in FIG. 5. This position of FIG. 7 is achieved byreassembling the parts with the locating ring positioned with its hole92 in engagement with the pin 88. To achieve a still smaller range ofcross-port leakage accommodation,

the locating ring 78 may be positioned as shown in FIG. 8 with the hole94 engaged with the pin 88. This positions the grooves 72 in registerwith the slots 64 for an even smaller arc of registration In any of thethree assembled positions just described, the valve may be adjusted toaccommodate exactly the cross port leakage ofa particular motor byadjustment of the screw 82 and spring 84. In this way, the increments offlow through the valve 44 which result from predetermined increments ofdelivery line pressure may be precisely adjusted over a much wider rangethan would be possible if only one are of register between the groovesin the spool and the slot in the body were available.

We claim:

l. A valve for automatic stabilization of hydraulic motor speed undervarying load conditions comprising a body having a longitudinal boreclosed at opposite ends, first and second lateral ports opening to thebore at longitudinally spaced locations, the first port communicatingwith the bore through slots of limited circumferential width, a spoolslidable in the bore having a land to normally close communicationbetween the ports, tapered grooves in the land adapted to register withthe slots in the bore when the spool is shifted longitudinally toestablish communication between the ports, piston means at one end ofthe bore for shifting the spool, spring means at the opposite end of thebore to bias the spool toward closed position, means forming a slidingkey and keyway between the spool and the bore to maintain rotationalregister between the slots and the grooves, and means for establishing aplurality of positions of register to provide a plurality of maximumflow rates when the spool is fully shifted to open position.

2. A valve as defined in claim 1 wherein the bore is formed by a sleevein the body, the sleeve having longitudinal slots adjacent the firstport.

3. A valve as defined in claim 2 wherein a locating member has a slidingkeyed relation with the spool and a plurality of selective keyedrelations with the body.

4. A valve as defined in claim 3 wherein the locating member is a ringpositioned between the body and an end cap removably attached to thebody.

1. A valve for automatic stabilization of hydraulic motor speed undervarying load conditions comprising a body having a longitudinal boreclosed at opposite ends, first and second lateral ports opening to thebore at longitudinally spaced locations, the first port communicatingwith the bore through slots of limited circumferential width, a spoolslidable in the bore having a land to normally close communicationbetween the ports, tapered grooves in the land adapted to register withthe slots in the bore when the spool is shifted longitudinally toestablish communication between the ports, piston means at one end ofthe bore for shifting the spool, spring means at the opposite end of thebore to bias the spool toward closed position, means forming a slidingkey and keyway between the spool and the bore to maintain rotationalregister between the slots and the grooves, and means for establishing aplurality of positions of register to provide a plurality of maximumflow rates when the spool is fully shifted to open position.
 2. A valveas defined in claim 1 wherein the bore is formed by a sleeve in thebody, the sleeve having longitudinal slots adjacent the first port.
 3. Avalve as defined in claim 2 wherein a locating member has a slidingkeyed relation with the spool and a plurality of selective keyedrelations with the body.
 4. A valve as defined in claim 3 wherein thelocating member is a ring positioned between the body and an end capremovably attached to the body.